**Problem:**
Grafana still can't mount PV correctly in Cloud, because there are 2
`securityContext` and `fsGroup` only work on Pod spec.

**Solution:**
Change the `securityContext` to Pod spec.

**Issue:**
https://github.com/rancher/rancher/issues/16953

This reverts commit cb0f92308e32c637a5cd09b5c1b7a644378bb58a.

Problem:
There isn't `fsGroup` in Container `securityContext`

Problem:
- Grafana can't mount PV correctly in Cloud

Solution:
- Use SecurityContext

Issue:
rancher/rancher#16953

        (+) Only use for Rancher 2.0 Monitoring and Alerting
        (+) Support Grafana to proxy with authorization bearer token to
        Prometheus-Auth agent
        (+) Support Prometheus web to proxy with authorization bearer token
        to Prometheus-Auth agent
        (+) Rich metrics for Kubernetes and Rancher
Co-authored-by: aiwantaozi <michelia.feng@gmail.com>
Co-authored-by: orangedeng <jxfa0043379@hotmail.com>